Giant Clams are large traps found within the Tide Pool, usually underwater.
When the Spelunker or any other Monster passes over its middle, usually containing some treasure or even an Idol as bait, it will snap shut, destroying anything caught in its jaws. Furthermore, standing on the top of the closed clam will prick you (or any enemies) for 1 point of damage, similar to the Thorny Vines found within the Jungle. The Clam is, as the name suggests, very large, being 3 tiles wide. Despite this, it only seems to snap shut when its middle is passed over, making a heist of the Golden Idol relatively safer. After a being closed for a few moments, it will reopen again.
It is unfortunately impossible to permanently disable Giant Clams[Needs Research], but if the treasure sitting atop it is desired, it is possible to throw something at or even shoot the treasure to knock it off its deadly pedestal. If you stand on the edge of the Clam, without touching the middle, you can also use your whip to dislodge the treasure.